The panel that came with my door has a label saying which side goes to the outside. There is no obvious reason why. Can anyone explain it?
I recently had a replacement panel made up for elsewhere, and that wasn't marked.
does it have "heat reflecting" coating?
Super hydrophobic coating only on the side intended to face outwards?
Or possibly the outside of the original had a self-cleaning coating.
Is it Pilkington K glass? It has a coating on the internal panel. Building inspectors have a gadjet which tells them if it is facing the right way but I was told that it doesn't make much difference to its effectiveness.
"Phil L" wrote in news:9Lb_A.102710$BB3.79213 @fx29.am4:
Contradicted here (Pilkington site) :
Pilkington K Glass? forms the inner pane of an energy-efficient IGU, such as Pilkington energiKare?. The coating reflects heat back into the room whilst also letting in free heat from the sun, known as passive solar gain.
Thanks. But on ordering I had the choice of 'special' glass or ordinary. Since it is surrounded by other glass panels chose 'ordinary' so it wouldn't look different.
Pilington K glass the IR coating is best off on the inside where it will suffer less wear and tear from wind, rain and window cleaners.
But superhydrophobic self cleaning coatings need to be on the outside of the building to cause rain to run off the window and away quickly.
it isn't the rain you need to run away
it's the bird ****
tim
If it only worked one way, that would contradict the Second Law of Thermodynamics. You would be able to use such a panel as a free heat pump. See also, Maxwell's Demon. I guess questions of durability of coatings are more significant on the orientation of the panel.
QA/QC requires a label - we're ISO certified we are
It works slightly better one way round. In practice avoiding damage to the coating is much more important. The fundamental point is that the outside is bright with energetic 6000K solar radiation whereas the inside of a house is typically more like 300K longwave IR.
It isn't hard to have a surface that blocks or reflects one without significantly affecting the other. Shallow angle total internal reflection at the coating to air interface alters the symmetry.
In an ideal world the coating would have an RI equal to sqrt(RIglass) for a perfect match. It doesn't so there is a slight mismatch.
Designer metamaterials have already been fabricated with anomoulous wavelength absorption profiles so that putting them out in the sunshine on a clear day causes them to get cooler. It loses heat at long wavelengths faster than it absorbs energy from solar radiation:
It isn't breaking the laws of thermodynamics though. It is in radiative equilibrium with the sky containing a small sun at 6000K and the rest of the sky with an effective temperature of about 80K.
one way mirror
They are not truly one way mirrors. They are half silvered with the room side very well lit and the observers side in near total darkness.
The laws of thermodynamics forbid anything that would allow you to make heat energy flow spontaneously from a cooler to a hotter body.
IIRC symmetry of transfer does not require symmetry of equilibrium temperatures in an asymmetric system so the temperature of the inner surface of the inner pane does depend on whether the reflective costing is on the inner or outer pane
or both sides lit the same, with the silvering over a dark under layer.
That doesn't line up with what is happening with double glazing. But this has become one of those threads, so I'll probably leave it & get back to today's pita job. Which you might notice I don't want to do.
NT
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